The invention relates to a method for separating monolithically produced laser diodes. It relates, in particular, to a method for separating laser diodes having mirror surfaces etched out of a semiconductor substrate wafer.
Semiconductor components can only be produced efficiently if a large number of chips can be prepared on a semiconductor substrate wafer. In the case of laser diodes for light waveguides this means that all technology-oriented steps are performed on the wafer, including the complex production of the laser mirrors. It has recently become possible to produce the laser mirrors on the wafer; this is done by means of so-called physical or physical-chemical dry etching processes. This manufacturing method is known under the generic term "monolithic laser technology".
For manufacturing the laser mirror the semiconductor surface to be protected is coated with a photoresist of the desired geometric structure. Through the process of dry etching the desired mirror, structure is subsequently obtained on the wafer. In the dry etching process, an interspace of predetermined width and depth is etched into the semiconductor. Portions of the interspace walls represent the laser mirrors. The mirror height must meet the minimum requirement that the light can emerge unhindered from the laser diode. The interspace width between the mirrors of adjacent diodes can vary. At this stage of the manufacturing process, the p-contacts of the semiconductor diodes are already formed. To complete the process, one must break the wafer into separate chips and produce the n-contacts.
When conventional separation methods are used, the following problems occur: if separation is attempted by scribing the wafer with a diamond, for example from the p-side, then the mirrors get damaged, if the mirror distance d is small (d.apprxeq.10 .mu.m). If the wafer is scribed from the reverse side with d being small, the yield will be poor due to adjustment inaccuracies and fracture dislocations which can cause the finished laser mirrors to get separated from the diodes.
The same problems are encountered, if the wafer is only slightly scribed and then split. In all cases, the yield is modest. On the other hand, however, the light cone, which emerges from the laser diode with an angular aperture of approximately 60.degree., can hardly be disturbed by a projecting fracture edge.
According to another alternative, technique the distance between mirrors of adjacent laser diodes is made very large (d&gt;50 .mu.m) so that scribing and breaking from the p-side as well as from the n-side proceeds without any problem. The disadvantage in this case is, however, that the light cone emerging from the laser diode is usually disturbed by reflections at the fracture edge. As a result, the far field is normally so distorted that the light cannot be coupled into a glass fiber in a defined manner and thus, the laser diode cannot be used as a light waveguide element.
It is an object of this invention to provide a method for separating monolithically produced laser diodes which avoids far-field-distorting fracture edges.
It is another object of this invention to provide a method for separating monolithically produced laser diodes which includes only a few steps and is relatively simple.
It is a further object of this invention to provide a method for separating monolithically produced laser diodes which renders high yields.
It is still a further object of this invention to provide a method which improves over existing processes to separate laser diodes.